Every time these arguments come up, whoever is arguing against the GTVA starts from a position of how everything possible goes wrong and assumes that as what will happen. I admit I tend to stray a bit too far in the other direction, but still, the GTVA failing to block every single node as the Shivans move? If the Shivans had shown an inclination to move on other systems, you can bet Command would have been hurrying quite a bit faster to shut those nodes. Shivans get to Epsilon Pegasi, shut the next layer of nodes. Information travels faster than ships ever can, and as a position is lost, the next steps up. Maybe during the SSI they would have succeeded in getting through. Maybe. Certainly not now.
When the node shuts, the fleet can easily deal with any isolated Shivan remnants.
Re-read the FS1 briefings and such. The Shivans hold no interest in planets, going instead for control of subspace nodes and transit points to planets' direct exclusion. Ships coming through a node are easy prey for Mjolnirs and blockades. Ships heading toward nodes are easy prey for Mjolnirs and blockades. Ships staging between nodes are easy prey for bombers. The NTF end-run through the series of blockades to Gamma Draconis shows just how deadly blockades are to masses capital ships in rapid transit. Yes, the SJ Sathanas smashes a blockade to get to where it's going in Bearbaiting, but that blockade was ill informed of the juggernauts abilities. Defending a node means that the GTVA picks exactly where and how a fight goes down, and can stack all the advantages against the Shivans. A tactical reserve of the new corvettes allows Command to hunt down and destroy any ship that escapes before the blockade is destroyed, and when the blockade is lost, the transit to the node to assist in the defense or move to the next system in, if necessary.
And again it all comes down to time. An effective blockade nets the GTVA precious minutes to bring node closers into position. Minutes are all it takes, and the new ships and tactical doctrines of the GTVA net a lot of minutes in the form of savaging the front end of the Shivan column. Those "torn, divided, and disorganized bunch of spare ships" we've already seen completely destroy a Sathanas and its entire escort (provided the escort existed. I'm inclined to think it did), once again, with zero losses.
Don't be so quick to discount the Titan destroyers. They may not have the straight up firepower of a Raynor, but they can damn well take care of themselves. Witness the Temeraire against the four Shivan destroyers between Frankenstein's Monsters, Forced Entry, and Preserving the Balance, and how it nearly effortlessly wipes the floor with all of them. Eight next generation destroyers, plus an untold number of new corvettes, which in conjunction have been shown to mop the floor with Sathanases. You can't tell me those are ineffective against the Shivans, because they obviously are.